Sealed vented insert spinneret



Aug. 20, 1968 J. DE JARNETTE BURKE, JR. ETAL 3,397,427

SEALED VENTED INSERT SPINNERET Filed Sept. 27, 1966 INVENTORS JAMES D ARNETTE BURKE, JR. CURTIS EN HAWKINS BY ,Q/ F

ATTORNEY United States Patent 3,397,427 SEALED VENTED INSERT SPINNERET James De Jarnette Burke, Jr., Kinston, and Curtis Owen Hawkins, Cove City, N.C., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Sept. 27, 1966, Ser. No. 582,321 Claims. (Cl. 188) ABSTRACT OF THE DISCLOSURE A spinneret for the production of hollow filaments that includes a shaped insert swaged into each passage of the spinneret to effect a seal between the insert and spinneret. The insert has an upper portion through Which polymer flows and a vented lower portion around which polymer flows.

This invention relates to spinnerets and, more particularly, to a spinneret for the production of hollow filaments from synthetic polymers.

There have been various types of spinnerets proposed for the spinning of hollow filaments, and generally these include an insert fitted in the spinneret passage to provide an annular space at the outlet for the formation of the sheath of the hollow filament. The interior of the filament is prevented from collapsing by introducing a gas or drawing air into the center of the filament by means of passageways in the insert.

While prior art efforts to obtain a satisfactory spinning nozzle for the spinning of hollow filaments have been somewhat successful, the variables introduced into filament wall thickness due to unbalanced polymer flow into the passage of the spinneret outlet present serious limitations. In addition, the insert-type spinnerets of the prior art are susceptible to polymer leakage into the core fluid supply passageways because of a lack of a positive seal between the polymer and core supply fluid. Furthermore, because of the non-aligned passage arrangement it is virtually impossible to visually inspect the polymer passages of the prior art spinnerets for pluggage without removing the insert.

Therefore, it is an object of this invention to provide a spinneret for the production of hollow filaments wherein a uniform polymer flow into the passage at the spinneret outlet is obtained. Another object of this invention is to provide a spinneret for the production .of hollow filaments wherein the filament wall thickness is accurately and consistently controlled.

Another object of this invention is to provide an inserttype hollow filament spinneret that has an improved seal between the polymer and core supply fluid passageways. A further objective of this invention is to provide an inserttype hollow filament spinneret wherein visual inspection can be made through the polymer passage without removing the insert.

The objects of this invention are accomplished by providing a spinneret formed from a plate. The upper and lower surfaces of the plate are connected by a passage having successive cylindrical, tapered and capillary lengths. An insert is fitted in the passage to form an extrusion orifice at the outlet of the passage. The insert has an upper cylindrical portion coextensive with the cylindrical length of the passage and a lower cylindrical portion projecting from the upper cylindrical portion substantially through the capillary length of the passage. The upper cylindrical portion of the insert has an axial bore partially through it and a plurality of radially spaced holes in communication with the bore and the tapered length of the passage to provide a polymer flow path through the spin- 3,397,427 Patented Aug. 20, 1968 neret. There are communicating passageways through the plate and the insert for supplying fluid to the interior of the hollow filament formed by extruding plastic material through the passage of the spinneret.

The invention will be further illustrated by reference to the accompanying drawings in which:

FIGURE 1 is a section view through a spinneret according to the invention.

FIGURE 2 is a section view of the insert of FIGURE 1.

FIGURE 3 is a bottom view of the insert of FIGURE 2.

FIGURE 4 is an enlarged partial section of FIGURE 1.

Referring now to the drawings, spinneret 10 is adapted to be mounted in a conventional filter pack for supplying a polymer composition to be spun into a filamenLThe spinneret 10 is formed from a plate 11 and is provided with a passage, connecting its upper and lower surfaces, that includes a first cylindrical length 12 terminating at shoulder 14, and a tapered length 16 continuing from shoulder 14 to a capillary length 18. An insert 20 is swaged into this passage and held in position by lip 23 which is formed as the insert is flared into the passage. The insert includes a first cylindrical portion 22 and a second cylindrical portion 24 continuing from the bottom surface 21 of the first cylindrical portion. The cross sectional dimensions of portion 24 are smaller than the capillary length 18 of the spinneret passage, thus forming a spinning orifice having the desired width of the wall of the filament to be spun. The insert 20 is also provided with a comparatively large central axial bore 26 that extends partially through the insert and terminates in a flat surface 30. Holes 32 lead straight through from flat surface 30 to bottom surface 21 of the insert and are substantially equispaced radially from the axis of bore 26 to provide uniform polymer flow into the continuous passage formed by cylindrical portion 24 of the insert 20 and capillary length 18. It can be readily seen that the alignment of the bore 26, holes 32, tapered length 16 and capillary length 18 of the spinneret passage allows for visual inspection of the polymer passage of the spinneret. This is normally done by shining a light into the polymer entrance to the spinneret and inspecting the capillaries at the outlet by observing them through a microscope. The insert 20 is provided with a lower axial bore 28 which connects to a lateral bore 34. When the insert 20 is fitted in the spinneret as shown in FIGURES 1 and 4, the bore 34 is aligned with a lateral bore 36 extending through the spinneret 10. The combined bores 36, 34 and 28 form a continuing passageway for supplying fluid to the interior of the hollow filament. When swaged in position, surface 21 of the insert 20 engages shoulder 14 in the bore of the spinneret 10 and the upper surface 25 of insert 20 is engaged by lip 23. In this manner, a positive seal is formed between the insert 20 and the spinneret to prevent leakage of the polymer into the core supply passageways 36, 34 and 28.

In operation, the molten polymer composition moves initially into bore 26 of insert 20 then it is uniformly distributed through holes 32 and passes through the passageway defined by cylindrical portion 24 of the insert 20 and capillary length 18 to form a hollow filament. As the polymer coalesces around the outlet end of insert 20, a partial vacuum is formed causing a gravity flow of room air through the combined bores 36, 34 and 28 into the center of the filament. The percentage of filament void can be controlled by capillary geometry, polymer viscosity and the rate of spinning and quenching. While in the preferred embodiment of this invention the holes 32 are shown equispaced radially it is also comprehended that they may also be equispaced both radially and circumferentially. The spinneret .of this invention may be made from metals known in the art, such as stainless-steel or platinum group metals.

The condensation polymers and copolymers, for example, polyesters, polyamides and polysulfonamides, and particularly those that can be readily melt-spun, are preferred in the practice of this invention. It is obvious that gas, preferably inert, may be used rather than room air to yield hollow filaments. It is also obvious that, while this invention has been illustrated for round cross-section filaments, other filaments whose outer surface cross-sections are non-round (i.e. trilobal, tetralobal, serrated, etc.) may be produced.

The spinneret of this invention has the advantage of being simple in construction while providing a means to accurately control the filament wall thickness, provide a positive seal between the insert and spinneret and enable visual inspection of the polymer passages without removing the insert from the spinneret.

It is to be understood that the embodiment disclosed may be altered and numerous other embodiments can be contemplated without departing from the spirit and scope of the appended claims.

What is claimed is:

1. A spinneret for the production of hollow filaments comprising:

(a) a plate having upper and lower surfaces connected by a passage, said passage having successive cylindrical, tapered and capillary lengths; and

(b) an insert including first and second cylindrical portions, said first cylindrical portion having a bottom surface and being swaged into said cylindrical length, said upper surface adjacent said passage being formed into a lip engaging said first cylindrical portion, said second cylindrical portion projecting from said bottom surface substantially through the capillary length and being of smaller cross-sectional dimensions than the capillary length, said first cylindrical portion having an axial bore partially therethrough and a plurality of radially spaced holes in communication with said bore and the tapered length of the passage through the plate, thereby providing a flow path through the spinneret, there being an axial bore through said second cylindrical portion, said axial bore being in communication with a source of fluid whereby to supply said fluid to the interior of a hol= low filament formed by extruding plastic material through said passage.

2. The spinneret of claim 1 wherein said cylindrical length terminates in a' shoulder, said bottom surface engaging said shoulder.

3. The spinneret of claim 1 wherein said holes in communication with said bore and said tapered length are equispaced radially from the aXis of said bore.

4. The spinneret of claim 1 wherein the axial bore partially through said first cylindrical portion has a flat bottom surface.

5. The spinneret of claim 1 wherein the tapered length of the passage is conical.

References Cited UNITED STATES PATENTS 3,014,237 12/1961 Breen 188 3,075,242 1/ 1963 Grafried 18-8 3,081,490 3/1963 Heynen et al 188 3,121,254 2/1964 Heynen et a1 l8-8 3,197,812 8/1965 Dietzsch et al 18-8 FOREIGN PATENTS 272,802 1951 Switzerland. 972,932 10/ 1964 Great Britain.

WILLIAM J. STEPHENSON, Primary Examiner. 

